An analogous example:
A particle can be at rest at v = 0)" alt="t = 0\v = 0)" />.
A nano-jiffy later it is moving due to some acceleration.

Imagine the motion of the same particle.
Let describes the motion of the particle. Consider the motion from to .Can we find at . In other words, if a function is defined on the closed interval [a,b], can it be differentiable on one of its end-points e.g.'a'?